1. Field of the Invention
The present invention relates to a reference signal generation circuit for generating a reference signal used in synchronous detection for removing an excitation signal component in an angle calculation section that converts a detection angle θ obtained from two-phase resolver detection signals output from a resolver for detecting a motor rotation angle, to a digital output angle φ, and relates to an angle converter and an angle detection apparatus having the reference signal generation circuit.
2. Description of the Related Art
In tracking loop angle calculation sections (resolver-digital converters, hereinafter called RD converters) for converting a detection signal θ obtained from two-phase resolver detection signals output from a resolver of the type of one-phase-excitation and two-phase-output, to a digital output angle φ, the detection angle θ is converted to the digital output angle φ by making a control deviation sin(θ−φ) zero. To obtain this control deviation sin(θ−φ), it is necessary to remove an excitation signal component from the resolver detection signals. To remove the excitation signal component, synchronous detection is performed with an excitation signal sin ωt being used as a reference signal.
The excitation signal component included in the resolver detection signals generally has a phase difference Δω from the excitation signal sin ωt for various reasons. Therefore, if synchronous detection is performed with the excitation signal sin ωt being used as a reference signal, the loop gain of the angle detection section is reduced. Therefore, it is desirable that the phase difference Δω be compensated for.
Japanese Registered Patent No. 3,442,316 (Japanese Patent Laid-Open No. 2000-353957) discloses a method for compensating for such a phase difference Δω. FIG. 9 shows the configuration described in Japanese Registered Patent No. 3,442,316.
In this configuration, two-phase resolver detection signals sin θ sin(ωt+Δω) and cos θ sin(ωt+Δω) output from a resolver are input to an absolute value comparator 11 and also to a switch 12. The output of the absolute value comparator 11 is sent to the switch 12 as a switching signal. The switch 12 is connected to an edge detector 13 for detecting rising and falling edges. The output of the edge detector 13 is input to a synchronizing circuit 14.
An excitation signal sin ωt sent to the resolver is input to a 90 degree and 270 degree signal generator 15 and to a phase adjustment range setter 16. The 90 degree and 270 degree signal generator 15 generates trigger signals indicating the positions of 90 degrees and 270 degrees from rising edges of the excitation signal sin ωt and sends the trigger signals to the phase adjustment range setter 16. Although the operation of the phase adjustment range setter 16 is not explicitly described, its output is input to the synchronizing circuit 14 to synchronize the excitation signal sin ωt with an edge of a rotation detection signal. With such a configuration, the synchronizing circuit 14 outputs a reference signal sin(ωt+Δω), obtained by shifting the excitation signal sin ωt by the phase difference Δω.
As described above, in Japanese Registered Patent No. 3,442,316, the two-phase resolver detection signals are used to generate the reference signal synchronized with the two-phase resolver detection signals to compensate for the phase difference.
In the method described in Japanese Registered Patent No. 3,442,316, however, because the reference signal is generated by zero-crossing edge detection of the signal sin θ sin(ωt+Δω) (or cos θ sin(ωt+Δω), obtained by amplitude modulating the reference signal by sin θ (or cos θ), the higher the angular velocity at which the resolver rotates, the more the amplitude-modulated waveform is distorted. As a result, the reference signal cannot be generated with the correct phase.
In addition, an edge detection signal at zero crossing also causes a phase shift due to noise intruding in actual use.